Assessment of flood management systems' flexibility with application to the Sacramento River basin, California, USA

Water resources managers and researchers have concluded that increasing system flexibility will provide flood management systems advantages in meeting objectives under uncertain future hydrologic conditions. However, despite the frequent use of the term flexibility, demonstration of the concept to analysis and design of flood management systems has yet to be conducted. Building upon previous studies of flexibility in the fields of information technology and social-ecological systems, among others, we outline an approach to investigate how structural and non-structural flood management actions relate to system flexibility. We assess flexibility using metrics that describe flexibility by five characteristics: slack, redundancy, connectivity, adjustability, and compatibility/cooperation. We apply this flexibility assessment to four proposed flood management strategies, each with a unique suite of management actions, for the Sacramento River basin in California, USA. The foci of benefits differ between the four different flood management strategies, with varying emphasis on protecting urban communities, rural and agricultural improvements, and ecosystem restoration. The suite of proposed structural and non-structural actions has the potential to increase all five flexibility characteristics, though only a selection of actions are included in each of the four management strategies. The flexibility assessment reveals a disproportionate emphasis in all strategies on increasing slack in the current system as well as a concentration of expenditures towards structural versus non-structural components. Only two of the assessed strategies improve all five flexibility characteristics, and these two strategies also include the greatest number of actions that provide flexibility benefits. We do not find a clear link between these more flexible strategies and their time and cost-effectiveness in terms of reduction in damages. The outlined method provides a useful tool for comparing the flexibility of potential management strategies, and further application can provide more insight into broader thinking on flood management under uncertainty.